diff --git a/lib/mongo/ObserveMultiplex.js b/lib/mongo/ObserveMultiplex.js
index 7a086974..36e889bc 100644
--- a/lib/mongo/ObserveMultiplex.js
+++ b/lib/mongo/ObserveMultiplex.js
@@ -189,13 +189,9 @@ _.extend(ObserveMultiplexer.prototype, {
             if (!self._handles) return;
 
             // First, apply the change to the cache.
-            // XXX We could make applyChange callbacks promise not to hang on to any
-            // state from their arguments (assuming that their supplied callbacks
-            // don't) and skip this clone. Currently 'changed' hangs on to state
-            // though.
             self._cache.applyChange[callbackName].apply(
                 null,
-                EJSON.clone(args)
+                args
             );
 
             // If we haven't finished the initial adds, then we should only be getting
@@ -221,7 +217,7 @@ _.extend(ObserveMultiplexer.prototype, {
                 // We silence out removed exceptions
                 if (callback === 'removed') {
                     try {
-                        callback.apply(null, EJSON.clone(args));
+                        callback.apply(null, handle.nonMutatingCallbacks ? args : EJSON.clone(args));
                     } catch (e) {
                         // Supressing `removed non-existent exceptions`
                         if (!isRemovedNonExistent(e)) {
@@ -229,7 +225,8 @@ _.extend(ObserveMultiplexer.prototype, {
                         }
                     }
                 } else {
-                    callback && callback.apply(null, EJSON.clone(args));
+                    callback && callback.apply(null,
+                    handle.nonMutatingCallbacks ? args : EJSON.clone(args));
                 }
             });
         });
@@ -249,8 +246,8 @@ _.extend(ObserveMultiplexer.prototype, {
         self._cache.docs.forEach(function(doc, id) {
             if (!_.has(self._handles, handle._id))
                 throw Error('handle got removed before sending initial adds!');
-            var fields = EJSON.clone(doc);
-            delete fields._id;
+            const { _id, ...fields } = handle.nonMutatingCallbacks ? doc
+                : EJSON.clone(doc);
             if (self._ordered) add(id, fields, null);
             // we're going in order, so add at end
             else add(id, fields);
@@ -259,7 +256,9 @@ _.extend(ObserveMultiplexer.prototype, {
 });
 
 var nextObserveHandleId = 1;
-export function ObserveHandle(multiplexer, callbacks) {
+
+// When the callbacks do not mutate the arguments, we can skip a lot of data clones
+export function ObserveHandle(multiplexer, callbacks, nonMutatingCallbacks = false) {
     var self = this;
     // The end user is only supposed to call stop().  The other fields are
     // accessible to the multiplexer, though.
@@ -279,6 +278,7 @@ export function ObserveHandle(multiplexer, callbacks) {
     });
     self._stopped = false;
     self._id = nextObserveHandleId++;
+    self.nonMutatingCallbacks = nonMutatingCallbacks;
 }
 
 ObserveHandle.prototype.stop = function() {